Recently I've been testing opengl and directx and I've found that directx with dxvk (Vulkan) on linux brings about 20% more fps at 3840x2160@144hz. While having darker and slightly more realistic vision, with airfields ("plates") not standing out from terrain so much. But the downside is that mirrors are working only in opengl mode. Affected planes: La-7, british fighters, german naval bomber with 4 mirrors nobody flys, twin engined american fighters, possibly others. Opengl seems to be supported better and in many games have better multi-textures, like sky in Unreal Gold being transparent, while in Directx it's purple... In Il-2 "perfect" landscape visibility (72km) seems to be allowed only for opengl. On some of the settings both renders draw landscape with "squares", but that could be AMD implementation. Back in the day nvidia paid to Oleg Maddox big money and we have what we have with best settings only for nvidia.

Another thing is playing at 1920x1080 seems better than at 4k. Fps dips to 0 are less frequent and contact dots (up to 16 km away) are more noticeable in the former case, about 4 times bigger. They are barely visible in 4k without zooming in.